The present invention relates to an arrangement in for driving an automatic selector appliance of a motor vehicle change-speed gearbox into a position for a forward gear specified for emergency running in the event of failure of an electronic control unit, and, more particularly to an arrangement comprising a selector actuator operable to select forward gear by the engagement of at least two frictional selector connections and being driven by pressure medium, a pressure pump for generating a system pressure of a two-positional directional selector valve for subjecting the selector actuator to the system pressure, a main-pressure control valve for regulating the system pressure or is derived from such a regulated pressure.
In a known arrangement described in WO 88/01029 A1, the emergency control valve is held in its shut-off position, in which a selection of the third gear specified for emergency running is not possible in the case of a fault, by its self-retention function, which is maintained by the system pressure. In order to permit the emergency running control valve to be switched over in the event of a fault, the driving engine (and with it the pressure pump generating the system pressure) must be switched off with the vehicle at rest so that the emergency running control valve is moved into its emergency running position by its spring reset. When the driving engine is restarted with the emergency running control valve in its emergency running position, i.e. in the N position of the range selector valve, the system pressure which is now again available is fed to the control part of a selector valve so that the selector valve, which is in its basic position, is switched over. As a result, a connected selector actuator for the third gear is subjected to system pressure. When the range selector valve is subsequently moved into the D position, the other selector actuators of the third gear, of which one is directly connected to the range selector valve and two are connected to it via associated selector valves, are subjected to system pressure. Switching off the driving engine, after the electronic control unit has already failed, can lead to dangerous driving conditions, particularly because this action has also switched off the auxiliary energy for steering forces, braking forces and the like.
An arrangement for driving an automatic selector appliance of a change-speed gearbox with four forward gears is shown in U.S. Pat. No. 5,191,815. In the event of a failure or of a fault in the electronic control unit, the third gear is immediately selected and the working pressure for the selector actuators is set immediately to the highest value.
DE 41 32 873 C2 describes an automatic selector appliance for a change-speed gearbox of the epicyclic type which operates with a frictional selector (clutch or brake), which can be engaged by a selector actuator of the axial piston type, between two gear elements which can rotate relative to one another, with a selecter valve for subjecting the selector actuator to pressure and with an electromagnetic switch-over control valve which can be controlled by an electronic control unit and is used for switching over a selector valve. In this known selector appliance arrangement, both the selector valve and the switch-over control valve can be respectively switched over between a rest position, which can be selected by spring force, and a working position. The selector actuator is connected to a pressure-relieved null connection in the rest position of the selector valve and, in the working position is connected to a system pressure conduit carrying a control system pressure. A selector valve control connection used for switching over into the rest position is connected to a pressure-relieved null connection in the rest position of the switch-over control valve and, in the working position of the switch-over control valve, is connected to a control pressure supply conduit leading to a control pressure.
The selector actuator which has just been actuated must remain subjected to working pressure in this known selector appliance even in the case of a failure of the electrical voltage supply. When the engine is switched off, the selector appliance should take up such a position that the selector actuators remain unpressurized when the engine is restarted. For this purpose, the known arrangement is such that the selector valve can be additionally actuated into its rest position by the control pressure of the switch-over control valve and can be additionally actuated into its working position by a control pressure which depends on the pressure of the selector actuator and has appropriate control connections.
In addition, the known arrangement is such that the switch-over control valve is only brought into its working position in phases but is, on the other hand, in its rest position in the non-transient condition of the selectors, i.e. when these selectors are fully engaged or fully disengaged. Moreover, a control valve has a valve connection for a control pressure conduit leading to the control connection of the selector valve for driving it into the working position, a valve connection for a control pressure conduit leading to the control connection of the selector valve for driving it into the rest position, a valve connection for a control pressure conduit leading to the switch-over control valve and a valve connection for pressure relief.
The control valve of this known arrangement is switchable over between a rest position, on one hand, in which the valve connection for the control pressure conduit for actuating the selector valve, in the rest position of the latter, is connected to the valve connection for pressure relief. In contrast, the valve connection for the control pressure conduit to actuate the selector valve, in the working position of the latter, is connected to the valve connection for the control pressure conduit leading to the selector valve, and on the other hand, a working position in which the valve connection for the control pressure conduit for actuating the selector valve into the rest position is connected to the valve connection for the control pressure conduit leading to the selector valve. The valve connection for the control pressure conduit for actuating the selector valve is connected, in the working position of the latter, to the valve connection for pressure relief. Furthermore, this known arrangement is such that the control valve is switched over as a function of the condition of the selector so that the valve connection of the control valve for the control pressure conduit leading to the switch-over control valve is positively connected in one non-transient condition of the selector to the valve connection for the control pressure conduit for switching the selector valve over into its position which brings the selector into the other nontransient condition.
Because of this configuration, the switch-over control valve is always located in its rest position in the non-transient condition of the selector in the case of the known selector appliance. Consequently, an electronics or voltage failure does not change anything in the selection condition. In the disengaged condition of the selector, the selector valve is held in its rest position by spring force and, in the engaged condition, is held in its working position by the self-retention effect of the relevant control pressure, which depends on the pressure of the selector actuator. The control valve is always precontrolled, as a function of the respective instantaneous non-transient condition of the selector, so as to adopt that position in which, on excitation of the switch-over control valve, the selector valve is switched over into the position for the respectively other selection condition, i.e. the one which is not non-transient at that instant. When the engine is switched off, the pressure supply is also switched off so that the selector valve and the control valve are moved into their respective rest positions by spring force. As a result, the selector actuators unpressurized when the engine is restarted.
In order to control the control valve as a function of the non-transient condition of the selector, the known selector appliance actuates the control valve into each of its two positions by a positional control pressure and has appropriate control connections. A positional control valve has a valve connection for a control pressure conduit leading to the control connection of the control valve for moving the latter into the rest position, a valve connection for a control pressure conduit leading to the control connection of the control valve for moving the latter into the working position, a valve connection for a control pressure feed conduit carrying a control pressure and a valve connection for pressure relief. The positional control valve is switchable over between a rest position, on one hand, in which the valve connection for the control pressure conduit for actuating the control valve, in the rest position of the latter, is connected to the valve connection for the control pressure feed conduit and the valve connection for the control pressure conduit for actuating the control valve, in the working position of the latter, is connected to the valve connection for pressure relief, and a working position, on the other hand, in which the valve connection for the control pressure conduit for actuating the control valve into its rest position is connected to the valve connection for pressure relief and the valve connection for the control pressure conduit for actuating the control valve into its working position is connected to the valve connection for the control pressure feed conduit.
The known arrangement moves the positional control valve by spring force into its rest position and into its working position by a control pressure which depends on the pressure of the selector actuator. The control valve is additionally actuatable into each of its two positions by a control pressure which depends on the switch-over control valve and has relevant control connections. The control connection of the control valve is connected, for the movement of the latter into the rest position, to the control pressure conduit leading to the selector valve for the movement of this latter valve into the working position by the control pressure which depends on the switch-over control valve and for the control connection of the control valve, for the movement of the latter into the working position by the control pressure which depends on the switch-over control valve, to be connected to the control pressure conduit leading to the selector valve for the movement of this latter valve into the rest position by the control pressure which depends on the switch-over control valve.
The Automobile Technical Journal 85 (1983), 6, pp. 401-405 discloses another arrangement for the control of an automatic selector appliance of a gear shifter of a motor vehicle which is already different from the arrangement of the present invention in that a special emergency running control valve is not included. If with this known arrangement a security function is called for, as for example is the case if going beyond the maximum engine speed or an interruption of electrical transmissions occurs, the transmission then switches into idle, the spring-loaded magnetic valves move into switching portion "3". With this known arrangement during idle position, the position "neutral" and "rearward" may be chosen hydraulically by means of the drive lever.
DE 24 38 249 discloses an electronic control apparatus especially for a gear shifting arrangement in automatic transmissions of motor vehicles with a combustion engine which provides for a security device to prevent the overstepping of the allowable maximum speed. Contrary to the arrangement in accordance with the invention for an automatic selector appliance, the here known electronic drive device does not include a special emergency running control valve. However, this electronic drive device does include an arrangement for switching off the other part of the drive device if the maximum allowable speed of the engine is exceeded, whereby the highest gear is engaged following the switching off of the drive device. This feature is to prevent any danger during operation of the motor vehicle in case of a parting of a cable or during shut-down of the entire electronic drive device. With this type of break-down it should thus at least be possible to drive to the closest service station using one of the gears. The driver should not be in a position to limit the running steps to a much lower speed or to have to engage the rearward speed during an excessively high motor vehicle speed. It is especially to be avoided during malfunctioning of the electronic drive device or of the speed control sensor that the engine oversteps if too low a gear is engaged, that is to say the maximum allowable speed of the engine was exceeded.
U.S. Pat. No. 4,976,171 discloses an arrangement different in kind for the control of an automatic selector appliance of a motor vehicle drive transmission, which allows for the operation of a shift lever from a p-range into a drive-range only if the service brake was first used.
An object of the present invention is to avoid the occurrence of unsafe driving conditions when selecting the forward gear specified for emergency running in an arrangement for driving a selector appliance into a position for emergency running.
The foregoing object has been achieved in an advantageous manner in accordance with the present invention, by providing that the valve inlet of the range selector valve is configured to be put under system pressure and is connected to the valve outlet of the emergency running control valve for indirectly subjecting the selector actuator to pressure. The range selector valve has a valve outlet connected to the control pressure connection of the emergency running control valve and valve connections corresponding with the valve outlet. One of the valve connections is arranged to operate as a pressure-relieved null connection and the other of the valve connections is arranged to be continuously put under a system pressure. The valve outlet is exclusively connected, in the P position, to a corresponding one of the valve connections, which initiates, on a basis of pressure level thereof, switch-over of the emergency running control valve into the emergency running position and is connected to the other corresponding one of the valve connection in other positions of the range selector valve. The self-retention function of the emergency running control valve is usable for the emergency running position, and the control pressure for the maintenance of the self-retention function is derivable from the pressure level at the valve outlet of the emergency running control valve for indirectly subjecting the selector actuator to pressure.
In the arrangement according to the present invention, it is unnecessary to switch off the driving engine for the purpose of switching over the emergency running control valve into its emergency running position. On the contrary, the vehicle can be brought to rest with the engine running in order to put the range selector valve into the parking position P. The emergency running control valve is switched over into its emergency running position by this manual selection of the P position of the range selector valve. This, of course, is only possible when the vehicle is at rest because of the positive connection with the parking brake. Because the at-rest condition of the vehicle is imposed for this purpose, no unsafe driving conditions are possible during the subsequent selection of the forward gear specified for emergency running by actuation of the range selector valve into its D position.
Another advantageous feature of the present invention is a simplification of the valve construction of the emergency running control valve. In particular, the self-retention function of the emergency running control valve is provided by a 3/2-way shuttle valve in which one valve connections of two associated valve connections configured to be shut off alternatively relative to the first-mentioned valve connection is connected to the valve outlet of the range selector valve configured for connection to the control pressure connection of the emergency running control valve. The other valve connection of the two valve connections of the shuttle valve is configured to be shut off and connected to the valve outlet of the emergency running control valve for indirectly subjecting the selector actuator to pressure. A third valve connection of the shuttle valve is configured to remain open permanently and is connected to the control pressure connection of the emergency running control valve.
An advantageous simplification of the control measures for the emergency running is accomplished by providing that at least one of the selector actuators of the forward gear usable for emergency running is subjected to system pressure independently of the range selector valve and the emergency running control valve and is alone subjectable to system pressure because, in the condition where no current or pressure is supplied, the basic setting of the respectively associated selector valve and control valve when the selector appliance is brought into the emergency running position.
A special emergency running control valve can be advantageously omitted because its function is transferred to another control valve of the selector appliance. Specifically, a gear-retention control valve is the emergency running control valve in which two valve outlets are respectively connected to one valve connection of the selector valve of a selector actuator of the forward gear specified for emergency running. In two end positions thereof, the gear-retention control valve connects a valve inlet thereof, which is under system pressure, to a valve outlet thereof associated with the respective end position and connects another valve outlet to a pressure-relieved null connection. One valve connection of the selector valve is connected to one valve outlet of the gear-retention control valve and is connected in its basic position to a selector actuator which is subjected to system pressure both in the forward gear specified for emergency running and in a further forward gear. The other valve connection of the selector valve is connected to a valve outlet of the gear-retention control valve and is connected in its basic position to a selector actuator which is subjected to system pressure in the forward gear specified for emergency running but is pressure-relieved in the further forward gear. The selector actuator, which is pressure relieved in the further forward gear, is connected to the valve connection of a second selector valve which is connected, in the basic position of the second selector valve, to a further valve connection of the second selector valve. The further valve connection is subjected to a system pressure via a valve connection of a connected second gear-retention control valve in a basic position thereof, and the connection between the selector actuator which is pressure-relieved in the further forward gear and the respectively affected valve connection of the two selector valves occurs via a 3/2-way shuttle valve, with the permanently open valve connection being connected to the selector actuator.
An advantageous pressure supply is provided to the range selector valve when the emergency running control valve is switched over in the system pressure of the valve connection of the range selector valve, is arranged to be continuously put under a system pressure and corresponds with the valve outlet of the range selector valve connected to the control pressure connection of the emergency running control valve. The system pressure of the valve connection is lowered relative to the system pressure regulated by the main pressure control valve.